This invention relates generally to an electrophotographic printing machine, and more particularly concerns an apparatus for permanently affixing a powder pattern to a sheet of support material.
Electrophotographic printing records an electrostatic latent image of an original document on a photoconductive member by exposing the charged portion of the photoconductive member to a light image of the original document. A development system moves a developer mix of carrier granules and toner particles into contact with the latent image. The toner particles are attracted electrostatically to the latent image forming a toner powder image thereon. This toner powder image is, then, transferred to the sheet of support material.
Multi-color printing repeats the foregoing processes a plurality of times. However, each development cycle deposits differently colored toner particles onto the sheet of support material. These toner particles are transferred, in superimposed registration with one another, creating a colored copy corresponding to the original document. The fusing operation permanently affixes the multi-layered toner powder image to the sheet of support material. In addition to permanently affixing the toner powder image, the fusing powder image must also form transparent layers to appropriately modulate the light rays transmitted therethrough so that the copy has the composite colors of the original document.
Numerous types of fusing devices have heretofore been developed. In particular, multi-color electrophotographic printing machines have employed fusing devices which heat the conveyor belt transporting the sheet of support material so as to raise the temperature thereof and minimize heat loss thereto. In addition to heating the conveyor belt, a radiant energy source furnishes heat energy to the toner particles. This permanently affixes the toner particles to the sheet of support material and produces transparent colored layers attenuating the light rays passing therethrough to form a color copy of the original document. U.S. Pat. No. 3,781,516 issued to Tsilibes, et al. describes a control system for the foregoing type of fusing apparatus. U.S. Pat. No. 3,826,892 issued to Draugelis, et al. in 1974 and U.S. Pat. No. 3,781,517 issued to Skamara in 1973 also relate to this type of a fusing apparatus. In all of the foregoing patents, a heated conveyor belt advances the sheet of support material, with the toner particles thereon, through the fuser passageway. Under these thermal conditions, the belt frequently relaxes and creeps relative to the support and drive rollers. This reduces the frictional force between the drive rollers and belt introducing relative movement or slippage therebetween. Slippage of this type may result in the support material remaining in the fuser passageway an inordinate length of time resulting in sheet scorching.
Accordingly, it is a primary object of the present invention to improve the fuser conveyor belt so as to prevent slippage between the drive roller and the belt.